1. Field of the Invention
The described invention relates to microfluidic structures. More specifically, it relates to the pumping of microfluidic structures using a peristaltic bubble pump.
2. Description of Related Art
Micro-electromechanical systems (MEMS) provide a technology that enables the miniaturization of electrical and mechanical structures. MEMS is a field created primarily in the silicon area, where the mechanical properties of silicon (or other materials such as aluminum, gold, etc.) are used to create miniature moving components. MEMS can also be applied to GaAs, quartz, glass and ceramic substrates.
An example of a MEMS device could be a small mechanical chamber where two liquids (biofluids, drugs, chemicals, etc.) are mixed and a sensor interprets the result. MEMS could also be integrated with logic functionalities i.e. having a CMOS circuit to perform some algorithm with the data provided by the sensor. The CMOS circuit could then have circuit elements that transport the results of the algorithm and the sensor input to another device.
One of the mechanical processes typically performed by MEMS is transporting small amounts of fluids through channels. One way to do this is through the use of a variety of mechanical and non-mechanical pumps.
Mechanical pumps include piezo-electric pumps and thermo pneumatic peristaltic pumps. These pumps typically use a membrane which, when pressure is exerted on the membrane, restricts or allows fluid flow as desired. These pump structures with membranes, however, are relatively complex to manufacture.
Non-mechanical pumps include electrokinetic pumps. Electrokinetic pumps use an ionic fluid and a current imposed at one end of the channel and collected at the other end of the channel. This current in the ionic fluid impels the ionic fluid towards the collection pad of the electrokinetic pump.
Another type of non-mechanical pump uses a thermal bubble to pump fluids through a microchannel. FIGS. 1A and 1B show a prior art example of a thermal bubble pump used to pump a fluid. A controllable heater (not shown) above the pump chamber 1 causes a bubble 4 to expand or shrink. A nozzle-shaped inlet 2 and a nozzle-shaped outlet 3 create a net flow from the inlet 2 to the outlet 3. FIG. 1A shows an example in which an expanding bubble 4 causes a net flow out of the main chamber 1 through the outlet 3. FIG. 1B shows an example in which a shrinking bubble 4 causes a net flow into the main chamber 1 through the inlet 2. The shape of the nozzle-shaped inlet 2 and outlet 3 bias the direction of fluid flow; however, the efficiency of the bubble pump is fairly low as a backflow through both the inlet 2 and outlet 3 occurs.